1. Field
The present invention relates to an antistatic antireflection film, a method for manufacturing the antistatic antireflection film, a polarizing plate and an image display device.
2. Description of the Related Art
In image display devices such as a cathode ray tube (CRT) display device, a plasma display panel (PDP), an electroluminescent display (ELD), a vacuum fluorescent display (VFD), a field emission display (FED) and a liquid crystal display device (LCD), an antireflection film is generally disposed on the outermost surface of a display in order to prevent lowering of contrast caused by the reflection of external light or glare of an image.
In addition, the antireflection film is used for the outermost surface of the display, and thus it is required to have a high scratch resistance or abrasion resistance. Further, it is required to have excellent antifouling properties (resistance to attachment of stains or wipeability of stains when adhered) against various stains such as primarily fingerprints in exhibition or daily use.
As the basic configuration of an antireflection film, it is known that on a transparent support, the antireflection film has a low refractive index layer having a refractive index lower than that of the support and a predetermined thickness, and in order to obtain the above-mentioned characteristics, various antireflection films have been proposed as the composition and configuration of the low refractive index layer or other layers.
For example, Japanese Patent Application Laid-Open No. 2008-169364 describes a curable resin composition including an ethylenically unsaturated group-containing fluorocopolymer and a (meth)acryloyl compound having a fluorine atom as a substituent and further including particles having a hollow or solid silica as a main component, a compound having a polydimethylsiloxane structure and a fluorine-based surfactant. A cured material obtained from the curable resin composition has a low refractive index and an excellent scratch resistance and antifouling properties, and an antireflection coating having a low refractive index layer formed of the cured material is described in Japanese Patent Application Laid-Open No. 2008-169364.
Further, Japanese Patent Application Laid-Open No. 2010-085983 describes a composition for a low refractive index layer including hollow silica fine particles and an organic binder containing a polyfunctional monomer which has three or more reactive functional groups in a molecule thereof and contains no fluorine atom, a fluorine atom-containing monomer and a fluorine atom-containing polymer, and further including an antifouling agent containing a fluorine atom and a silicon atom. As an optical film having a low refractive index layer formed by the composition for a low refractive index layer on the outermost layer thereof, an optical film having at least one of a low reflectance and an excellent scratch resistance and a magic wiping durability is described in Japanese Patent Application Laid-Open No. 2010-085983.
Meanwhile, in an optical film such as an antireflection film, it is also known to install a hardcoat layer having antistatic properties and hard coat properties in order to prevent scratches on the surface or the attachment of dust and the like.
For example, in order to obtain a film having antistatic properties and hard coat properties, it is known to form a hardcoat layer by using a compound having a quaternary ammonium salt group as an antistatic agent and a composition containing a polyfunctional monomer to be a binder (for example, Japanese Patent No. 4600605).
In order to obtain an antireflection film having excellent antireflection properties, antistatic properties and hard coat properties and more advanced scratch resistance, abrasion resistance and antifouling properties, it is possible to contemplate an antireflection film in which a low refractive index layer is provided on an antistatic hardcoat layer.
The present inventors have studied and thus could find out that when a composition having a quaternary ammonium salt group is used to form a hardcoat layer, antistatic properties are excellent, but when a low refractive index layer is formed on the hardcoat layer by a composition including a fluorine-containing compound as described in Japanese Patent Application Laid-Open No. 2008-169364 and Japanese Patent Application Laid-Open No. 2010-085983, scratch resistance deteriorates and furthermore a surface defect occurs in which the low refractive index layer becomes white turbidity.
In consideration of these circumstances, an object of the present invention is to provide an antistatic antireflection film having excellent antireflection properties and antistatic properties, no surface defect, and excellent scratch resistance, abrasion resistance and antifouling properties.
Further, another object of the present invention is to provide a manufacturing method of the antistatic antireflection film, a polarizing plate using the antistatic antireflection film and an image display device having the antistatic antireflection film or the polarizing plate.
From the viewpoint of obtaining a low refractive index layer having a low refractive index and an excellent scratch resistance, abrasion resistance and antifouling properties, it is appropriate to use a fluorine compound such as specific fluoropolymer and fluorine-containing polyfunctional monomer or silica fine particles and a specific siloxane compound in a composition for a low refractive index layer. In order to solve the problems, the present inventors have studied, and thus, found out that when a low refractive index layer is formed on a hardcoat layer including a compound having a quaternary ammonium salt group, adhesion with the hardcoat layer deteriorates if a monomer having a plurality of —CF3 groups as a fluorine-containing polyfunctional monomer and a low surface free energy is contained in the molecule of a fluorine-containing compound of a composition for a low refractive index layer, thereby degrading scratch resistance and generating white turbidity on the coating film of the low refractive index layer. Although the reason is not fully understood by the mechanism, it is speculated that if a fluoromonomer to be added to the low refractive index layer in order to improve the scratch resistance for a hardcoat layer containing a compound having a quaternary ammonium salt group which is very hydrophilic in structure is very hydrophobic, the affinity would deteriorate. The present inventors have studied, and as a result, found out that the deterioration in scratch resistance and white turbidity may be suppressed by using a monomer having four or less —CF3 groups, a high surface free energy and many reactive functional groups as a fluorine-containing monomer.
That is, the problem of the present invention may be solved by the following means.